Fail-safe aircraft instrument and servo stabilizer therefor

ABSTRACT

A fail-safe servo pneumatic indicating system is provided wherein the pneumatic drive is connected to the indicator of the instrument through a first gear train. The motor of the servodrive is connected, by a second gear train, to an intermediary gear of the first gear train. The synchro of the servodrive is mounted to the shaft of the above-mentioned intermediary gear. A stabilizer is provided which comprises an impact element riding with the indicator shaft and mounted for a predetermined amount of free rotary movement relative to the shaft so that it will provide kinetic energy to the system in opposition to kinetic energy imparted to the system upon incidence of oscillation of the indicator.

United States Patent [72] Inventor James W. Angus Baldwin, N.Y. [21Appl. No. 803,722 [22] Filed Mar. 3, I969 [45] Patented June 1, I971[73] Assignee Kollsman Instrument Corporation Syosset, N.Y.

[54] FAIL-SAFE AIRCRAFT INSTRUMENT AND SERVO STABILIZER THEREFOR 7Claims, 4 Drawing Figs.

[52] US. Cl 73/386, 73/430 [51] InLCI ..G0ld 11/10, G071 7/12 FieldofSeareh 73/388, 384, 386, 430

[56] References Cited UNITED STATES PATENTS 3,009,357 11/1961 Andresen,Jr. 73/384 Primary Examiner-Louis R, Prince Assistant Examiner-.losephW. Roskos Attorneys-E. Manning Giles, .I Patrick Cagney, Peter S.

Lucyshyn and Richard G. Kinney ABSTRACT: A fail-safe servo pneumaticindicating system is provided wherein the pneumatic drive is connectedto the indicator of the instrument through a first gear train. The motorof the servodrive is connected, by a second gear train, to anintermediary gear of the first gear train. The synchro of the servodriveis mounted to the shaft of the above-mentioned intermediary gear. Astabilizer is provided which comprises an impact element riding with theindicator shaft and mounted for a predetermined amount of free rotarymovement relative to the shaft so that it will provide kinetic energy tothe system in op- 7 position to kinetic energy imparted to the systemupon incidence of oscillation of the indicator.

PATENIED'JuM nan 3,5 1; 571

" sum 10F 2 BY 0770 NE) PATENTED JUN 1 191:

SHEET 2 OF 2 FAIL-SAFE AIRCRAFT INSTRUMENT AND SERVO STABILIZEIRTHEREFOR BACKGROUND OF THE INVENTION Fail-safe instruments are known tothe art and one such system, for example, is shown in US. Pat. No.3,160,012 entitled Fail Safe Aircraft Instrument. Briefly, there isdisclosed an aircraft instrument having an indicator shaft which isdriven both by a pressure-responsive pneumatic-drive mechanism and by anelectrical servosystem. The servosystem includes a drag-cup motor and asynchro control transformer, each having a rotor mechanically connectedto the indicator shaft. In operation, the pneumatic driving means actsto position the indicator according to a given parameter.Simultaneously, an electrical computing system accounts for known errorsin the parameters used by the pneumatic-drive system and directs theservosystem to cause the drag-cup motor to drive the output shaft untilthe position of the output shaft, as sensed by the synchrorotor-corresponds to the required value determined by the electricalcomputing system.

While instruments constructed in accordance with the teachings of theabove-identified patent' have performed satisfactorily, there is an everincreasing need for devices of this type which are more compact andwhich utilize drive mechanisms characterized by extremely low frictionso that when the pneumatic-drive mechanism operates alone to drive theindicator pointer, errors will not be introduced as a result of frictionin the system.

While it is desirable to maintain low friction in the drive mechanismsof the system, low-friction mechanisms are sub ject, at times, to acondition of undesirable oscillation. That is, under certaincircumstances, if a shock is introduced to the system (either mechanicalor electrical), the system is subject to sustained oscillation.

Accordingly, a need exists for a compact fail-safe servo pneumaticinstrument wherein the level of internal inertia and friction is kept toa minimum and wherein means are provided to attenuate the system toservo stability SUMMARY OF THE INVENTION In accordance with the presentinvention, an improved failsafe servo pneumatic indicating system isprovided comprising an output shaft, low-friction drive mechanismrotatably positioning the shaft, the drive mechanism including theelectrically actuated servo drive mechanism and a pressure-responsivepneumatic-drive mechanism interconnected in an operating relationshipwherein the servo drive mechanism normally overrides the pneumatic-drivemechanism to apply a servo corrected movement to the output shaft andwherein the pneumatic-drive mechanism acts to apply an approximatemovement to the output shaft upon failure of the servo drive mechanism,and stabilizing means comprising an impact element riding with the shaftand mounted for a predetermined amount of free rotary movement relativethereto to provide an opposing impact thereto upon the incidence ofoscillation of the low-friction drive mechanism.

In the presently preferred embodiment of the invention, a firstlow-friction gear train connects the pneumatic-drive mechanism to theoutput shaft, a second low-friction gear train connects the dragcupmotor to an intermediary gear of the first gear train, the rotor of thesynchro transformer being directly mounted to the shaft of theintermediary gear. Thus, there is provided a compact fail-safe servopneumatic indicating system wherein the driving system is characterizedby extremely low friction so as to minimize errors when the system isoperating in its penumatic-drive mode.

One of the important features of the present invention relates to animpact element riding with a high-speed shaft and mounted for apredetermined amount of free rotary movement relative thereto to providean opposing impact thereto upon the incidence of oscillation of saidlow-friction drive mechanism.

Other features and advantages of the invention will be apparent from thefollowing description and claims and are illustrated in the accompanyingdrawings which show structure embodying preferred features of thepresent invention and the principals thereof, and what is now consideredto be the best mode in which to apply these principals.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic view showing afail-safe servo pneumatic altimeter constructed in accordance with thepresent invention;

FIG. 2 is a perspective view of a stabilizing element incorporated inthe altimeter shown in FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view taken approximately asindicated on the line 3-3 of FIG. 2 and showing the pin mountingthereof; and

FIG. 4 is a top plan view of the rotatable portion of the stabilizer inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT ON THE PRESENT INVENTIONReferring first to FIG. 1, the instrument incorporates an aneroid systemcomprising a diaphragm-type pressure capsule 2 which expands andcontracts responsive to static pressures applied thereto.'The output ofdiaphragm 2 acts through a suitable linkage 6 to rotate shaft 4, whichis fixed to gear sector 8. Preferably gear sector 8 and its pinion 10are such that a full deflection of the diaphragm 2 will result inapproximately full rotation of pinion l0. Rotation of the pinion 10 istransferred to rotary motion of shaft 14 through the gear train 12.Preferably gear train 12 is such that shaft 14 will rotate one rotationfor each I ,000 feet of altitude.

It is known that certain characteristic errors are introduced to thepneumatic-drive mechanism and that these errors can be predicted. Tocorrect for these errors it has been the practice to utilize a servodrive system including a drag-cup motor and a synchro controlledtransformer, which normally overrides the pneumatic-drive system. Inaccordance with this practice, synchro control transformer 18 receivessignals from a remote onboard computer (not shown) and directs thedragcup motor 16 to apply torque to position the indicator 17 indefiance of the torque produced by the pneumatic-drive system.

Heretofore, it has been the practice to mount the rotor of the drag-cupmotor 16 directly to the output shaft 14. In accordance with one aspectof the present invention, the dragcup motor 16 is shown to one side ofthe system so as to enable the length of the altimeter housing (notshown) to be shortened by at least the length of the motor. Thisarrangement also has the advantage of materially reducing the inertia ofthe system and, correspondingly, increasing the accuracy of thepneumatic-drive mode of operation. It will be noted that when electricaloperation is selected, the repositioning of shaft '14 by the torque ofmotor 16 results from the biasing force which the motor provides againstthe aneroid capsules. The rotor of the drag-cup motor 16 may be ofaluminum, its mass being of the order gram.

Because the drag-cup motor 16 remains mechanically connected to theintermediary gear 22 of gear train 12 through a gear train 24, even whenthe electrical operation is not operative, it is important to minimizethe frictional effect of gear train 24 during the pneumatic mode ofoperation. This is accomplished in the illustrated embodiment whereingear train 24 is such that the ratio of rotation of shaft 27 to shaft 14is no greater than 2 to II.

In order to actuate motor 116 from a servosystem, a synchro controltransformer 18 has a rotor 26 mounted directly to shaft 28 of theintermediary gear 22 of gear train 112. The rotor" of synchro 18 has aweight of the order of% of a gram and has no friction-producing brushes.The portion of gear train 112 connecting the rotor of synchro 18 toshaft 114 is such that the rotor 26 will turn through 360 for a 10,000foot change in altitude. This permits a correction of errors in thepneumatic system of up to 5,000 feet.

The operation of the fail-safe servo pneumatic system is fully disclosedin the aforesaid patent. Suffice it to say that when the position ofpointer 17, as determined by the output of synchro 18, is different fromthe remote signal of the onboard computer, an error signal will bedelivered to an amplifier (not shown) which energizes the drag-cupservomotor 16 so that the torque thereof depends upon the magnitude ofthe error signal, while the direction of rotation of motor 16 dependsupon the sense of the error signal. When the error signal approacheszero, the altimeter indication will approach that determined by thecomputer. In the event of a power failure or electrical malfunction orwhen the servo becomes inoperative, the servo is deenergized and thealtimeter immediately returns to the diaphragm-sensed indication.

While it is desirable to keep the friction and inertia of the system atits lowest possible level, for the reasons explained above, if a shockis introduced either mechanically or electrically to the low-frictionsystem, the system may go into oscillation. In such cases, shaft 28turns the rotor 26 of the synchro 18 to a position'which is nearlystable (often referred to as a null). Because of the low friction of thesystem and lack of inertia dampers of the conventional design, andbecause the biasing forces against which the motor action operates isextremely small in such cases, a shock to the system often results inrapid low-amplitude oscillation of the indicator 17.

To eliminate this tendency of oscillation, a stabilizer 30 is mounted toa high-speed shaft in the system. In the preferred embodiment, asillustrated herein, the stabilizer is shown mounted to the output shaft14. It should be noted that shaft 27 also operates at sufficiently highspeed to accommodate a suitable stabilizer.

Referring to FIGS. 2-4 the stabilizer 30 comprises a disc 32 rigidlysecured to shaft 14. A thin shell 34 is loosely mounted atop disc 32 bya pair of pins 38 such that shell 34 has a limited freedom angle ofrotation. When the system is subjected to a high frequency,low-amplitude oscillation, shell 34 will act as a shock device. Thus, asthe shaft 14 moves in one direction, the pins 38 push the shell 34along. When the shaft 14 reverses its direction, the shell 34 continuesto move until the pins (now moving opposite) have traversed the angle arelative to the loose shell. Due to the opposite rotations at the pointof contact between the pins 38 and the loose shell 34, an impact resultswhich is made equal to the kinetic energy of the system at the centroidof the oscillation. The constraints are basically the matching of thekinetic energy level so that if the system gets into oscillation, itwill be attenuated within one cycle to a level that results in the decayof the oscillation to an undetectable level.

lt should be noted that in the operation above considered, the velocityof the element is the most significant factor and not the mass. To keepthe dead load on the system to a minimum the stabilizer 30 is configuredto concentrate the mass at its outer peripheral regions. Thus, the shell34 is of generally cup-shaped form and has an upstanding rim portionconstituting a substantial portion of its total mass. Thestabilizer 30is symmetrical to provide for dynamic stability and is provided with aplurality of symmetrically spaced impact points to prevent shear loadingat the bearing in which shaft 14 is pivoted.

While preferred construction features of the invention are embodied inthe structure illustrated herein, it is to be understood that changesand variations may be made by those skilled in the art without departingfrom the spirit and scope of the appended claims.

The embodiments of the invention in which an exclusive privilege orproperty I claim are defined as follows:

1. A fail-safe servo pneumatic indicating system having an output shaft,drive mechanism rotatably positioning said shaft, said drive mechanismincluding an electrically actuated servo drive mechanism and apressure-responsive pneumatic drive mechanism interconnected in anoperating relationship wherein said servo drive mechanism normallyoverrides said pneumatic drive mechanism to apply a servo correctedmovement to said output shaft and wherein said pneumatic-drive mechanismacts to apply an approximate movement to said output shaft upon failureof said servo drive mechanism, said servo drive mechanism including adrag-cup motor having a rotor and a synchro transformer having a rotor,said system being characterized by a first low-friction gear trainconnecting said pneumatic drive mechanism to said output shaft, saidfirst gear train having a shaft mounting an intermediary gear andconnected to the rotor of said synchro transformer by a separate secondlow-friction gear train independently connecting the rotor of saiddrag-cup motor to said intermediary gear.

2. In a fail-safe servo pneumatic indicating system, an output shaft,low-friction drive mechanism rotatably positioning said shaft, saiddrive mechanism including an electrically actuated servo drive mechanismand a pressure-responsive pneumatic drive mechanism interconnected in anoperating relationship wherein said servo drive mechanism normallyoverrides said pneumatic drive mechanism to apply a servo correctedmovement to said output shaft and wherein said pneumatic-drive mechanismacts to apply an approximate movement to said output shaft upon failureof said servo drive mechanism, and stabilizing means comprising animpact element riding with said shaft and mounted for a predeterminedamount of free rotary movement relative thereto to provide an opposingimpact thereto upon the incidence of oscillation of said low-frictiondrive mechanism, said impact element being configured to provide aplurality of symmetrically disposed impact points relative to saidoutput shaft.

3. in a fail-safe servo pneumatic indicating system, an output shaft,low-friction drive mechanism rotatably positioning said shaft, saiddrive mechanism including an electrically actuated servo drive mechanismand a pressure-responsive pneumatic-drive mechanism interconnected in anoperating relationship wherein said servo drive mechanism normallyoverrides said pneumatic drive mechanism to apply a servo correctedmovement to said output shaft and wherein said pneumatic-drive mechanismacts to apply an approximate movement to said output shaft upon failureof said servo drive mechanism, and stabilizing means comprising animpact element riding with said shaft and mounted for a predeterminedamount of free rotary movement relative thereto to provide an opposingimpact thereto upon the incidence of oscillation of said low-frictiondrive mechanism, said impact element having a configuration, symmetricalwith respect to the output shaft, and having a mass concentrationadjacent its outer periphery.

4. ln a fail-safe servo pneumatic indicating system, an output shaft,low-friction drive mechanism rotatably positioning said shaft, saiddrive mechanism including an electrically actuated servo drive mechanismand a pressure-responsive pneumatic-drive mechanism interconnected in anoperating relationship wherein said servo drive mechanism normallyoverrides said pneumatic-drive mechanism to apply a servo correctedmovement to said output shaft and wherein said pneumatic-drive mechanismacts to apply an approximate movement to said output shaft upon failureof said servo drive mechanism, and stabilizing means comprising animpact element riding with said shaft and mounted for a predeterminedamount of free rotary movement relative thereto to provide an opposingimpact thereto upon the incidence of oscillation of said low-frictiondrive mechanism, said impact element being of cup-shaped configurationsymmetrical with respect to the output shaft, having a massconcentration adjacent its outer periphery and providing a plurality ofsymmetrically disposed impact points relative to said output shaft.

5. In an indicating instrument that includes a servo drive mechanismhaving an axially rotatable shaft connected to determine the position ofan output indicator, stabilizer means for dampening oscillation of saidservo drive mechanism, said stabilizer means comprising impact meansfixed to rotate with said shaft, and an impact element disassociatedfrom said servo drive mechanism and carried by said impact means inrelatively rotatable captive relation therewith to impact with saidimpact means upon a predetermined amount of relative rotationtherebetween occurring upon the incidence of oscillation of said servodrive mechanism, said impact element having a mass sufficient to applyimpact kinetic energy substantially matched to the kinetic energy of theservo drive mechanism at the centroid of oscillation.

6. In an indicating instrument that includes a servo drive mechanismhaving an axially rotatable shaft connected to determine the position ofan output indicator, stabilizer means for dampening oscillation of saidservo drive mechanism, said stabilizer means comprising impact meansfixedto rotate with said shaft, and an impact element carried by saidimpact means in relatively rotatably captive relation therewith forimpacting with said impact means upon a predetermined amount of relativerotation therebetween, said impact element having a configuration,symmetrical with respect to said shaft, and a mass concentrationadjacent its outer periphery.

7. In an indicating instrument in accordance with claim 6 wherein saidimpact element comprises a generally cupshaped structure having a bottomwall portion provided with a plurality of arcuate slots, said impactingmeans including a plurality of pins extending parallel to said shaftthrough said slots.

1. A fail-safe servo pneumatic indicating system having an output shaft,drive mechanism rotatably positioning said shaft, said drive mechanismincluding an electrically actuated servo drive mechanism and apressure-responsive pneumatic drive mechanism interconnected in anoperating relationship wherein said servo drive mechanism normallyoverrides said pneumatic drive mechanism to apply a servo correctedmovement to said output shaft and wherein said pneumatic-drive mechanismacts to apply an approximate movement to said output shaft upon failureof said servo drive mechanism, said servo drive mechanism including adrag-cup motor having a rotor and a synchro transformer having a rotor,said system being characterized by a first low-friction gear trainconnecting said pneumatic drive mechanism to said output shaft, saidfirst gear train having a shaft mounting an intermediary gear andconnected to the rotor of said synchro transformer by a separate secondlow-friction gear train independently connecting the rotor of saiddrag-cup motor to said intermediary gear.
 2. In a fail-safe servopneumatic indicating system, an output shaft, low-friction drivemechanism rotatably positioning said shaft, said drive mechanismincluding an electrically actuated servo drive mechanism and apressure-responsive pneumatic drive mechanism interconnected in anoperating relationship wherein said servo drive mechanism normallyoverrides said pneumatic drive mechanism to apply a servo correctedmovement to said output shaft and wherein said pneumatic-drive mechanismacts to apply an approximate movement to said output shaft upon failureof said servo drive mechanism, and stabilizing means comprising animpact element riding with said shaft and mounted for a predeterminedamount of free rotary movement relative thereto to provide an opposingimpact thereto upon the incidence of oscillation of said low-frictiondrive mechanism, said impact element being configured to provide aplurality of symmetrically disposed impact points relative to saidoutput shaft.
 3. In a fail-safe servo pneumatic indicating system, anoutput shaft, low-friction drive mechanism rotatably positioning saidshaft, said drive mechanism including an electrically actuated servodrive mechanism and a pressure-responsive pneumatic-drive mechanisminterconnected in an operating relationship wherein said servo drivemechanism normally overrides said pneumatic drive mechanism to apply aservo corrected movement to said output shaft and wherein saidpneumatic-drive mechanism acts to apply an approximate movement to saidoutput shaft upon failure of said servo drive mechanism, and stabilizingmeans comprising an impact element riding with said shaft and mountedfor a predetermined amount of free rotary movement relative thereto toprovide an opposing Impact thereto upon the incidence of oscillation ofsaid low-friction drive mechanism, said impact element having aconfiguration, symmetrical with respect to the output shaft, and havinga mass concentration adjacent its outer periphery.
 4. In a fail-safeservo pneumatic indicating system, an output shaft, low-friction drivemechanism rotatably positioning said shaft, said drive mechanismincluding an electrically actuated servo drive mechanism and apressure-responsive pneumatic-drive mechanism interconnected in anoperating relationship wherein said servo drive mechanism normallyoverrides said pneumatic-drive mechanism to apply a servo correctedmovement to said output shaft and wherein said pneumatic-drive mechanismacts to apply an approximate movement to said output shaft upon failureof said servo drive mechanism, and stabilizing means comprising animpact element riding with said shaft and mounted for a predeterminedamount of free rotary movement relative thereto to provide an opposingimpact thereto upon the incidence of oscillation of said low-frictiondrive mechanism, said impact element being of cup-shaped configurationsymmetrical with respect to the output shaft, having a massconcentration adjacent its outer periphery and providing a plurality ofsymmetrically disposed impact points relative to said output shaft. 5.In an indicating instrument that includes a servo drive mechanism havingan axially rotatable shaft connected to determine the position of anoutput indicator, stabilizer means for dampening oscillation of saidservo drive mechanism, said stabilizer means comprising impact meansfixed to rotate with said shaft, and an impact element disassociatedfrom said servo drive mechanism and carried by said impact means inrelatively rotatable captive relation therewith to impact with saidimpact means upon a predetermined amount of relative rotationtherebetween occurring upon the incidence of oscillation of said servodrive mechanism, said impact element having a mass sufficient to applyimpact kinetic energy substantially matched to the kinetic energy of theservo drive mechanism at the centroid of oscillation.
 6. In anindicating instrument that includes a servo drive mechanism having anaxially rotatable shaft connected to determine the position of an outputindicator, stabilizer means for dampening oscillation of said servodrive mechanism, said stabilizer means comprising impact means fixed torotate with said shaft, and an impact element carried by said impactmeans in relatively rotatably captive relation therewith for impactingwith said impact means upon a predetermined amount of relative rotationtherebetween, said impact element having a configuration, symmetricalwith respect to said shaft, and a mass concentration adjacent its outerperiphery.
 7. In an indicating instrument in accordance with claim 6wherein said impact element comprises a generally cup-shaped structurehaving a bottom wall portion provided with a plurality of arcuate slots,said impacting means including a plurality of pins extending parallel tosaid shaft through said slots.